University:
Boston University
Course:
CAS AS 311 | Planetary Physics
Academic year:

2022
Views:

264

Pages:

14
Author:

Brenden Trevino

CME Buildup and Erup*on • Removal of overlying ﬁeld • Gradual rise of pre-‐CME ﬁeld commonly observed • Fast expulsion + ﬂare Radial Velocity and Density at 102500s ì reconnection jets Log(ρ) in corona cavity Vr in corona: magenta ≥ 500 km/s, red ≤ -500 km/s Flare Close-‐up • Current sheet forms and thins • Reconnec+on causes explosive dynamics • Magne+c energy converted to mo+ons, hea+ng, etc. • Fine structure only visible with AMR • Now: inves+ga+ng par+cle accelera+on in ﬂare plasmoids • Future: simulate ﬂare emission and compare with data Flare Reconnec+on Jets Black field lines (same in all frames); radial velocity (red < 0, blue > 0, max. Vr = 500 km/s) Dynamic Plasmoids in flare sheet Observed vs. Simulated Islands current density SDO/AIA images Energy Evolu+on • Time history of magne+c and kine+c energies – CME onset corresponds to start of breakout reconnec+on – “Take-‐oﬀ” corresponds to start of fast ﬂare reconnec+on Scaling with S: Energy • Basic onset and take-‐oﬀ evolu+on insensi+ve to S – Weak energy dependence on S (reﬁnement level x 2) • Erup+on dominated by MHD, E par++oning by kine+cs Eﬀects of Resolu+on on Flare Onset • First ﬂare X point appears BEFORE sharp rise in Kine+c Energy (erup+on) • Higher resolu+on (higher S) à earlier erup+on Erup+on Mechanism • Magne+c energy vs energy of corresponding “open” state – No evidence for ideal instability/loss of equilibrium – Resis+ve instability Roles of Reconnec+on • Ini*al breakout reconnec*on – Removes overlying ﬂux by transfer to adjacent system – Feedback loop between expanding core accelera+on and reconnec+on rate (exponen+al growth) • Flare reconnec*on – Forms ﬂux rope and accelerates CME – Enables system to relax to lower energy state – Accelerates electrons via shocks, plasmoids, ? • Feedback between breakout and ﬂare reconnec*on enhances both rates Comparison with Observa*ons Fast (Alfvénic) erup+on (most important test) Classic three-‐part structure: shell, cavity, core CME = ﬂux rope Post-‐erup+on loops form while CME liqs oﬀ Widening ﬂare ribbons at base of post-‐erup+on loops EUV and H-‐alpha remote brightenings from breakout reconnec+on (Sterling et al. 2001; SOHO) ü Proliﬁc plasmoid forma+on ü ü ü ü ü ü ü downward moving plasmoids in early impulsive phase (Sui, Holman & Dennis 2003; RHESSI) ü plasma blobs in ﬂare sheet (Takasao et al. 2011; SDO) ü plasmoid shrinkage may accelerate electrons (Drake et al. 2005; Guidoni et al., in prepara+on) Conclusions • Breakout model explains many important features of fast CMEs/erup+ve ﬂares • Fast reconnec+on dominated by plasmoid forma+on – Favors Drake mechanism for par+cle accelera+on • Self-‐consistent driving and forma+on of current sheets are crucial • Next steps: – – – – Scaling with magne+c Reynolds number S Incorporate parametrized kine+c-‐scale ﬂux breaking extend to 3D develop robust model driven by observed condi+ons Summary: Scaling to Ac+ve Regions tsim/tobs ≈ Bobsdsim / Bsimdobs ≈ 950 • Temporal es*mates – interval between reconnec+on onsets in breakout and ﬂare current sheets ≈ 25 s – interval between ﬁrst X pt and jet onset in ﬂare sheet ≈ 9 s – delay between jet onset and erup+on take-‐oﬀ ≈ 3 s – impulsive phase lasts 7-‐34 s • Spa*al es*mates – longest-‐lived preﬂare reconnec+on site moves down ~22 arcsec – comparable downward shiq in main impulsive-‐phase X pt – top of ﬂare arcade rises ~33 arcsec (≈ max. lower jet length) during peak impulsive phase